INT 8 - System timer

no input data

% related memory:

40:6C = Daily timer counter (4 bytes)

40:70 = 24 hr overflow flag (1 byte)

40:67 = Day counter on all products after AT

40:40 = Motor shutoff counter - decremented until 0 then

shuts off diskette motor

- ~INT 1C~ is invoked as a user interrupt

- the byte at 40:70 is a flag that certain DOS functions use

and adjust the date if necessary. Since this is a flag and

not a counter it results in DOS (not the ~RTC~) losing days

when several midnights pass before a DOS call

- generated 18.2 times per second by the ~8253~ Programmable Interval

Timer (PIT)

- normal INT 8 execution takes approximately 100 microseconds

- see ~8253~